This invention relates generally to systems and methods for detecting and quantifying leaks in test objects through the use of differential absorption techniques. More particularly, this invention relates to an improved leak detection system designed to compensate for or disregard the masking effects of background gas, moisture, etc., which can otherwise reduce system sensitivity and resolution.
Leak detection systems of the so-called differential absorption type are known in the art, for example, by reference to U.S. Pat. 4,772,789. In such systems, a selected test object such as a rocket engine or components thereof is internally charged or pressurized with a test gas chosen for its capacity to absorb light of a particular wavelength. The pressurized test object is then illuminated with a light source having a wavelength selected to correspond with the absorptive properties of the test gas, and a video camera is used to produce images of the test object. Any test gas leaking to the exterior of the test object will absorb light such that the camera image represents a composite of the test object and leaking gas, if present. Such composite image can be analyzed particularly by computer in comparison with a counterpart image generated with illumination at a nonabsorbing wavelength to identify and quantify gas leakage.
While differential absorption systems beneficially provide remote and noninvasive leak detection analysis with respect to test objects of virtually any size and shape, the read-out from such systems is sometimes masked by small background quantities of the test gas or other contaminants present within the camera image path. More specifically, in a leak test facility, residual quantities of the test gas are sometimes present in the foreground and/or background with respect to an illuminated test object, wherein such gas will absorb some of the illuminating radiation and thereby falsely contribute to system read-out. As a result, precise determination of the occurrence and location of small leaks may be difficult or impossible. Alternately, when a test object is monitored for leakage over a prolonged time period, test gas may accumulate about the test object and within the image path to obscure determination of actual leakage location or magnitude. Similarly, atmospheric contaminants such as particulate and/or water droplets disposed along the image path can absorb light and thereby reduce system sensitivity.
The present invention is therefore directed toward improvements in leakage detection systems of the differential absorption type, wherein the system compensates for light absorption attributable to background factors and thereby provides improved sensitivity with respect to actual test gas leakage from a test object.